Bovine Protein C Native Protein. Protein C is a vitamin K-dependent plasma glycoprotein that is cleaved to its activated form by the thrombin-thrombomodulin complex. Protein C in its activated form contains a serine protease domain and functions in degradation of the activated forms of coagulation factors V and VIII. Protein C is a vitamin K-dependent serine protease produced in the liver and made up of 2 polypeptide chains. The 62 kDa proenzyme is activated by thrombin bound to an endothelial surface receptor and the active enzyme cleaves factor Va and VIIIa and thus inhibits blood coagulation. The molecular weight of the active enzyme is 55 kDa and the normal concentrations in human plasma is approximately 1-3 ng/mL because of the very fa